It is known to utilise magnetic particles to capture an analyte in a solution under test. Conventionally, the magnetic particles are coated with a substance to which the analyte will attach. A sensor surface in contact with the solution is provided with a similar coating and a magnetic field is applied to urge the magnetic particles onto the surface. Analyte bound to the magnetic particles then becomes attached to the sensor surface also. Thus, magnetic particles that have picked up analyte become immobilised on the sensor surface. An inductor located near to the sensor surface is used to quantify the number of magnetic particles that are so immobilised. The inductor forms part of a resonant electrical circuit. The resonant frequency of this circuit is determined in part by the inductance of this inductor and the inductance of the inductor is determined in part by the quantity of immobilised magnetic particles.
In the investigation of cell organelles and measurement of intracellular proteins, cells need to be disrupted or lysed, releasing the intracellular components for study. Freeze-thaw methods are commonly used to lyse both bacterial and mammalian cells. These methods involve freezing a cell suspension using a dry ice/ethanol bath or freezer and then thawing the material at room temperature or 37° C. This method of lysis causes cells to swell and ultimately break as ice crystals form during the freezing process and then contract during thawing. Multiple cycles are necessary for effective lysis, and the process can be time consuming. However, the freeze/thaw methods have been shown to release proteins located in the cytoplasm of bacteria effectively, and are recommended for the lysis of mammalian cells in some protocols.
Another approach commonly used to disrupt cells is to solubilise the cell membrane using a detergent. This has the added advantage of releasing membrane bound proteins but may dissociate protein complexes. Classically, physical methods have been used to disrupt cells, such as grinding tissue in a pestle and mortar or using a blade either as a scalpel or a liquidiser. There are some inherent disadvantages to mechanical lysis methods such as localized heating within a sample leading to protein denaturation and aggregation.
Ultrasound has also been used as a method of physical cell disruption which is based on the generation of high frequency pulses of pressure. Sonication (i.e. the process of disrupting the cell using sound waves) generates heat which may denature proteins, so the process should be performed in an ice bath. Some studies have shown that lysis using detergents to solubilise the cell membranes is more efficient at releasing intracellular protein than ultrasound.